1. Field of the Invention
The invention relates generally to methods and apparatus for precisely aligning objects, such as solid state lasers and optical fibers, and permanently fixing aligned objects (independent of the technique used to perform the alignment) in a precise relationship to one another. More particularly, the invention relates to (a) methods and apparatus which use fiducial marks to align objects in a precise manner, and (b) methods and apparatus which facilitate fixing prealigned objects to a mounting device after first temporarily affixing the objects to another fixture. The invention provides for the "passive" alignment of objects, alignment using a combination of passive and "active" alignment techniques, and the ability to align objects so as to permit batch processing of a multiplicity of objects.
The terms "passive" and "active" as used herein qualify whether the alignment technique being utilized requires the activation of any component being aligned. Thus, for example, a "passive" technique for aligning a laser and a fiber would not require the laser to be turned on during the alignment process; whereas an "active" technique would require that the laser be turned on.
2. Description of the Related Art
Many prior art techniques exist for aligning a pair of objects. For example, U.S. Pat. No. 4,404,741, to Lebet et al, teaches methods and apparatus for aligning a part to a substrate. The substrate is disposed onto an X-Y table which is in turn disposed onto a surface over which it can slide to align the substrate with the part. The part is optically viewed when it and the substrate are being aligned.
Another technique for aligning an object (or parts) onto a substrate (and ultimately affixing the part thereto) is taught in U.S. Pat. No. 4,476,626, to Gumbert et al, which describes apparatus for transferring leadless components from a carrier to a given mounting position on a circuit board utilizing a punch and a suction pickup arrangement.
Yet another prior art technique for mounting electronic components onto predetermined positions on a circuit board is taught in U.S. Pat. No. 4,670,981, to Kubota et al. In this reference positioning of the parts is achieved by aligning suction pickup tubes to a predetermined location on the parts which are held in cavities in a jig.
All of the references cited hereinabove are examples of prior art concerned with aligning individual objects (such as electronic parts) to positions on a circuit board or substrate; rather than first aligning the objects to one another and then attempting to mount the objects (while maintaining their relative alignment) onto a mounting surface.
Still another technique for mounting objects onto a substrate is taught in U.S. Pat. No. 3,982,979, to Hentz et al. This patent describes an apparatus and method for positioning a plurality of semiconductor devices onto a substrate by feeding the parts through tubular rings. Using the techniques taught in Hentz et al, several hundreds of objects may be simultaneously positioned and adhered to a substrate.
Although dealing with the mounting and aligning of a plurality of objects on a substrate, the Hentz et al patent, like the other patents cited hereinbefore, does not deal with precisely aligning pairs of objects prior to positioning and mounting them on the substrate. Such an alignment capability would be particularly useful in assuring that optical components, e.g., solid state (e.g., GaAs) lasers and fibers, are properly aligned, and remain properly aligned, when being affixed to a mounting surface.
Still other inventions, such as those directed to determining the accuracy of placement of objects on a substrate (as in U.S. Pat. No. 4,776,088, to Biggs et al), describe techniques which use glass plates with marks (patterns) thereon to check the accuracy of the placement of objects by a placement apparatus.
Patterns are also used by Tanimoto et al, in U.S. Pat. No. 4,699,515, which describes an exposure apparatus for manufacturing semiconductor devices. A pattern on a photomask is aligned with a plurality of patterns formed on a wafer in a manner that detects and corrects misalignment between the photomask and wafer, and between the photomask and individual chips on the wafer.
Tanimoto et al is an example of a common method of aligning objects with high precision called "contact" lithography. As applied to semiconductor processing, contact lithography involves aligning a glass mask to a part, typically a patterned silicon wafer, to an accuracy better than one micrometer. The usual method of accomplishing this alignment involves the use of corresponding fiducial, i.e. registration, marks (patterns) on both the glass mask and the wafer; the mask is moved relative to the wafer until the fiducial marks are correctly positioned with respect to each other. Both fiducial marks are observed through the transparent glass mask during the alignment process with the aid of a suitable microscope.
Among the many possible fiducial marks are crosses, for example, a solid cross on the mask which may be aligned to a hollow cross on a wafer; and other patterns, such as those depicted in FIG. 5 of the Tanimoto et al reference. Cross type patterns may be "nested" so that when they are in perfect alignment symmetric gaps between the solid and hollow crosses may be observed. Since small differences in such gaps are easily detected, the alignment may be carried out in a highly precise fashion.
As indicated hereinabove, it is sometimes desirable (and/or necessary) to first align small parts with great precision, and then later to fix the positions of these parts so that their relative alignment does not subsequently change. The specific example cited hereinbefore, deals with optoelectronic components. It is often desirable to carry out such an operation quickly and automatically, so that the alignment and subsequent fixing can be accomplished at low manufacturing costs.
It is currently common practice to carry out the alignment of optoelectronic components such as solid state lasers and fibers, "actively", i.e., by turning on the laser and moving the fiber relative to it until the light output through the fiber is maximized. A fiducial mark alignment scheme would permit alignment in a highly precise fashion with the laser off, i.e., this scheme would provide "passive" alignment which is considerably cheaper than active alignment.
Accordingly, it would be desirable to provide a highly precise (in the micrometer range) passive alignment technique, suitable for aligning pairs of objects, in particular, optoelectronic components, prior to mounting the objects on a mounting surface.
It would also be desirable to provide methods and apparatus which combine both passive and active alignment techniques, in order to achieve an even higher degree of precision when aligning parts, as required by some applications, prior to mounting the parts. In particular, it would be desirable to be able to combine the active alignment techniques described hereinabove, with passive (fiducial mark based) alignment techniques, to, for example, first obtain an intermediate state of alignment (using the passive technique), with active alignment being reserved for a final adjustment step.
As for fixing aligned parts (independent of the way they are aligned), the prior art customarily employs methods which involve either cementing, e.g., by use of epoxy, or soldering. In either case there is a danger that the parts can move during the setting of the cement or, the freezing of the solder. The soldering process also carries with it the potential for degrading the performance characteristics of heat sensitive components, such as lasers.
Accordingly, it would be desirable to be able to ameliorate the problem of permanently fixing aligned objects without disturbing their relative positions, independent of the method used to achieve the initial alignment and without unnecessary heating of the objects.
In addition to all of the above, it would be desirable to provide batch processing techniques for optoelectronic components, wherein a multiplicity of parts was simultaneously aligned and subsequently separated; in this batch processing procedure the teachings set forth herein would be utilized in order to help keep manufacturing costs to a minimum.